Plasmons in a two-dimensional system were first reported by C. C. Grimes and G. Adams, in Phys, Rev. Lett. 36, 145 (1976) on the surface of liquid helium, and later by S. J. Allen, Jr., D. C. Tsui, and R. A. Logan in Phys. Rev. Lett. 38, 980 (1977) in the inversion layer of electrons at the interface of a metal-oxide-semiconductor field-effect transistor (MOSFET) shown in FIG. 1, and more recently by N. Okisu and T. Kobayashi, in Electron. Lett. 22, 877 (1986) at the heteroinferface of a A1GaAs/GaAs heterostructure. The plasmons are coupled to the radiation field by a conductive metal grating structure superimposed on a second semitransparent metal film, with the grating having a periodicity which is typically several micrometers as shown in a typical example illustrated in FIG. 1.
The grating appears as a short circuit for radiation polarized parallel to the plane of the grating, thereby reflecting nearly all of the radiation. For radiation perpendicular to the plane of the grating, there is modulation of the far-infrared field with the periodicity of the grating, resulting in the coupling of the plasma oscillations of the inversion layer electrons with wave vectors q=n2.pi./.LAMBDA., where n=1,2 . . . , to the radiation field. By passing current, I, through the device, far infrared radiation is produced at the wave vector q=2.pi./.LAMBDA.. Coupling of the plasmons and the radiation field at the resonance peak take place at large inversion-layer electron densities. Consequently, tuning the infrared radiation is possible only by varying the periodicity of the grating, which is not possible in the prior art as that is fixed at the time of fabrication, and by varying the two-dimensional electron concentration, which requires deposition of a gate electrode below the grating. Due to pinch-off effects, this gate limits the power density level that can be generated to low levels (.ltorsim.10.sup.-7 W/cm.sup.2).